1. Field of the Invention
The present invention relates to an apparatus and method for reception in a wireless communication system. More particularly, the present invention relates to an apparatus and method for estimating a Signal to Interference plus Noise Ratio (SINR) of a ranging signal in a wireless communication system.
2. Description of the Related Art
As known in the art, wireless communication systems were originally developed to provide voice service. As technology has evolved, wireless communication systems now provide data service and a variety of multimedia services in addition to the voice service. However, conventional wireless communication systems, which were developed to provide only voice services, have a narrow bandwidth and require a high service fee, thus failing to satisfy diversified user demands. Further, with the continued development of the wireless communication industry and an increase in user demand for Internet service, a need for a communication system that efficiently provides the Internet service increases. Accordingly, a broadband wireless communication system for efficiently providing an Internet service has been introduced.
The broadband wireless communication system uses Orthogonal Frequency Division Multiplexing/Orthogonal Frequency Division Multiple Access (OFDM/OFDMA). Thus, the broadband wireless communication system can provide high-rate data transmission by transmitting a physical channel signal using a plurality of subcarriers. A wireless access scheme for the broadband wireless communication system has been standardized by the Institute of Electrical and Electronics Engineers (IEEE) 802.16 standardization group, which is an international standardization group.
Ranging, which is a kind of random access process, is defined by the broadband wireless communication system. The ranging process can be classified into initial ranging, periodic ranging, bandwidth request ranging, handover ranging and the like. More particularly, the initial ranging and periodic ranging are used to estimate Signal to Interference and Noise Ratio (SINR) to determine and control signal power, to measure a propagation delay for frame synchronization and to detect a user who intends to access a system. If an error occurs in the SINR estimation, control of signal power may not function properly. Thus, a transmitted/received signal may act as interference to neighboring cells and cause deterioration not only to the ranging process but also to the entire performance of the communication system.
A ranging code (i.e., a code set) used during the ranging process is broadcast using an Uplink Channel Descriptor (UCD) message. A Mobile Station (MS) attempts ranging by transmitting a ranging code suitable to a purpose through a ranging region that is allocated through an uplink resource allocation message (i.e., aUL-MAP). A Base Station (BS) calculates timing and frequency offset and the like using a received ranging code, includes the offset correction value in a ranging response (RNG-RSP) message, and sends the RNG-RSP message to the MS.
As described above, ranging codes are classified corresponding to their purpose. However, when a different MS transmits the same ranging code, code collision may occur because an MS randomly selects one of several ranging codes. When the ranging codes collide, an SINR measured by a BS is reduced due to the code collision.
Also, a plurality of MSs, being in communication with one BS, each performs absolute time synchronization and attempt ranging. However, there is a timing offset in a ranging signal received by the BS depending on a location of the MS. When the timing offset is generated, an SINR measured by the BS is reduced.
Thus, in order to accurately estimate an SINR of a ranging signal, it is required to be robust, that is effectively immune to other codes attempting ranging at the same time. Furthermore, it is required to remove the influence of a timing offset caused by a propagation delay that is generated depending on a location of an MS attempting ranging.